Abstract

Note

This article was exposed to the machine translation from Ukrainian.

Background

In July, US scientists led by Shukhrat Mitalipov from Center for Embryonic Cell and Gene Therapy at the Oregon Health & Science University successfully carry out genetic modifications of human embryo. This was not the first such attempt, but was first conducted without side effects. From the ethical considerations genetically modified embryo made it possible to develop only a few days.

For this experiment, the researchers used a method CRISPR (clustered regularly interspaced short palindromic repeats. This method is used only for 5 years, although scientists can modify the genome for much longer time.

Briefly, DNA recombination technologies allow to insert certain genes in plasmids (circular DNA molecules) or a viruses. Then the cell / bacteria can produce whatever is needed. Thus, we reiterate that already viruses had learned billions of years ago - genetically modify infected cells to use in their needs. The use of viral vectors (specially modified viruses) makes it possible to provide a genetic therapy in humans.

CRISPR
- this is not the first method, which is used for such purposes, but compared with others it easier, faster, cheaper and more powerful.

How does this method work?

CRISPR is based on the fact that the chains of nucleic acid (DNA or RNA) sequence naturally bind with another complementary chains. The basis of this technology is complex CRISPR RNAs and specific proteins, the most widely used complex is named CRISPR-Cas9
1
.

Protein`s (Cas-9) task
is to "cut" DNA strand, that we want to change, in the place, where we want it.
RNA (CRISPR) task
is to replace this deleted DNA. CRISPR can change the structure of the gene by point mutations. For example, CRISPR gene can transform hemoglobin S (sickle cell hemoglobin) in the gene for hemoglobin A. In this case Cas-9 cut DNA strand in place of encoding hemoglobin S, instead of this part a short DNA sequence from normal hemoglobin A gene is set (
Fig. 1
).

In addition, CRISPR can also affect gene expression. This allows to regulate protein production - reduce, stimulate of completely "disable". This effect is due to changes in the noncoding part of the DNA that controls gene expression - CRISPR simply reconfigure this gene part.

CRISPR can be delivered to a living organism using viral vectors, lipid nanoparticles or other technics. Usually the goal is a special group of cells such as hematopoietic cells in the case of hemoglobin.

On the other hand, this method is not ideal. Sometimes nucleic acid sequences can be randomly modified that were not the objective. Also, each genetic modification should be carefully considered, since some genetic changes can trigger a bunch of unintended effects. Taken a simple example of hemoglobin S - this genetic defect that allows the body to be less vulnerable to malaria. Change it - and the benefits disappear. Moreover, scientists still do not know exactly to what results can lead a correction of a variant polymorphism.

How can it help in medical practice?

Currently in animal models has been shown that CRISPR helps the body to be less vulnerable to prostate cancer. With the help of this method was developed a simple method for rapid diagnostics of virus Zika or it can be used to modify genes in T-cells
3
,
4
.

The main role of this method can lie in the treatment of the most serious diseases. Although there still remain a lot of questions. Most diseases are not caused by certain genes but a groups of genes, and each increase the risk of the disease only slightly. In this case, we must modify too much DNA sequences. In addition to this, oddly enough, modification of lifestyle still has greater impact on a large number of diseases, rather than genetic modification. This is unlikely to change in the near (and not very near) future.

By the way, experiment with genetic modification of human embryo is published in «Nature». It has open access, so it can be read by anyone interested
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.